1. Field of the Invention
The present invention relates to a high frequency heating coil device which is inserted into a slotted hole of an object in order to heat the object. More specifically, the present invention relates to a high frequency heating coil device which is made flexible so as to be inserted easily into the hole of the object to be heated where there is an obstruction.
2. Description of the Prior Art
When a steam turbine casing, or the like, is fastened by a bolt, in order to ensure proper fastening, the bolt is first heated in order to be elongated, and then a nut is fastened. Also, when the steam turbine casing is opened for maintenance inspection, the bolt which fastens the turbine casing is heated in order to be elongated, and then the nut is unfastened.
As a means for heating the bolt, there is a known high frequency heating coil device in which a high frequency current is supplied to a coil. This high frequency heating coil device is formed in a slender bar shape. It is inserted into a slotted hole bored in the bolt along a central axis of the bolt in order to heat the bolt rapidly from its interior.
The high frequency heating coil device is used for the above mentioned bolt but in the steam turbine casing there often exists an obstruction above the bolt. In such a case, a rigid and linearly formed high frequency heating coil device in the prior art, having no flexibility, cannot be inserted into the hole of the bolt.
To solve such a problem, the inventors have previously proposed a high frequency heating coil device Japanese laid-open patent application No. Hei 7-114984) in which, although not shown, a magnetic substance is disposed between conductive tubes, which constitute U-shaped coils. The magnetic substance is sectioned into plural pieces so as to promote flexibility of the coil device. Thereby, if there is an obstruction near a bolt, the entire coil device can be bent in order to be inserted into a hole of the bolt. This also applies to when drawing the coil device out of the hole of the bolt.
In the prior art device mentioned above, however, the magnetic substance is sectioned into plural pieces so that upper and lower end faces of each piece of the magnetic substance are orthogonal to a central axis thereof. Hence, if adjacent end faces make direct contact with each other oblique motion between each piece becomes restricted so that the coil device bends poorly. On the other hand, in order to ensure enough flexibility, it is necessary to provide a gap between each piece of the magnetic substance. If such gap is provided, magnetic flux may leak from the gap and may lower the heating effect of the coil device.